1. Field of the Disclosure
The disclosure generally relates to point-to-point (PtP) wireless links, and more specifically to an outdoor unit (ODU) configuration incorporating a cross connect architecture.
2. Related Art
Conventional microwave backhaul architectures are generally implemented as either a split outdoor unit (split ODU) configuration or an all outdoor unit (all ODU) configuration. Conventional split ODU configurations are generally comprised of both an indoor unit (IDU) and an outdoor unit (ODU), where the IDU and the ODU are connected over a coaxial interconnect. The IDU in a conventional split ODU configuration typically includes a modem, a digital-to-analog converter (DAC) and a baseband-to-intermediate frequency converter. Under normal operation, these conventional split ODU configurations generally involve transmitting an analog signal, at an intermediate frequency (IF), over the coaxial interconnect between the IDU and the ODU.
In some instances, all ODU configurations have been used as an alternative to these conventional split ODU configurations. Conventional all ODU configurations include only an ODU, and thus do not include an IDU. The ODU therefore includes a modem, a DAC as well as a baseband-to-radio frequency converter.
All ODU configurations are generally implemented having either a superheterodyne architecture or a direct conversion architecture. The superheterodyne architecture, which has been a popular all ODU architecture in the area of mobile backhaul networking, typically utilizes an analog-to-digital converter (ADC) to sample a full signal bandwidth of interest. In particular, a series of passive and active components including transformers, mixers, amplifiers, attenuators, and active and passive filters are needed to down-convert the carrier radio frequency (RF) to either a low or high intermediate frequency (IF) for sampling, while also maintaining signal integrity. Conversely, with a direct conversion architecture, rather than using a single ADC to sample an IF signal, the carrier frequency is directly converted to two baseband signals, I and Q, which are then sampled by one or more ADCs.
Traditionally, the majority of consumer demand in the area of mobile backhaul networking has been directed to voice services. However, recently the market for mobile backhaul services has begun to change. In particular, the mobile backhaul space is experiencing a growing demand for increased capacity as well as a shift from voice services to data services. These factors are driving mobile backhaul networks towards high capacity Internet Protocol (IP)/Ethernet connections.
Similarly, mobile backhaul networking is experiencing a transition to fourth generation (4G) standard and Long Term Evolution (LTE) networks. This transition is also driving the need for higher capacity, and is moving more packet traffic onto mobile backhaul networks. It is because of this transition that the mobile backhaul space has begun to shift away from superheterodyne architectures and towards direct conversion architectures, which generally provide decreased power consumption, smaller size, and a lower cost of production.
Additionally, in an effort to meet the growing demand for increased capacity, mobile backhaul networks have begun to implement systems that can handle higher capacity communications. For example, some mobile backhaul networks have begun to utilize spatial multiplexing, and/or multiple-input multiple-output (MIMO) techniques. However, these high capacity communication, techniques generally require the use of multiple all ODU receivers. However, this approach can cause various I/Q mismatches, which may include, but are not limited, to phase and gain I/Q mismatch, group delays between the I and Q signals, and frequency select mismatches. Each of these I/Q mismatches can result in noise floors, which may prevent the all ODU receivers from operating at a high quadrature amplitude modulation (QAM).
Embodiments of the disclosure will now be described with reference to the accompanying drawings. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The drawing in which an element first appears is indicated by the leftmost digit(s) in the reference number